FR3146465A1 - Process for manufacturing a watertight, pasteurizable and sterilizable closure system for jars with separate lid, and closure system obtainable by the process - Google Patents

Abstract

A method of manufacturing a sealed, pasteurizable and sterilizable closure system for jars with a separate lid, and a closure system obtainable by the method The invention relates to a method of manufacturing a closure system (1), as well as to such a system obtainable by the method, comprising a lid (2) and a seal (3), positioned at the edge of an upper ring of a container (4) to be closed. The cover is made of multilayer material comprising two layers of PP framing an EVOH barrier layer, said cover comprising on its lower face (21), a circular groove (5) housing the seal, a central portion (23) of said cover forming a convex dome (23a) raised outwards before vacuuming and capable of becoming concave (23b) during vacuuming, while a circular groove (24) surrounding the convex dome (23a) is provided at the upper face (22) of the cover, the latter being furthermore provided, over its entire periphery, with a closing rim (6) comprising closing notches (61). Figure for abstract: Fig.1

Description

Process for manufacturing a watertight, pasteurizable and sterilizable closure system for jars with separate lid, and closure system obtainable by the process

The present invention relates to the general field of containers used in the food industry and, more particularly, to glass containers, such as jars, intended to be hermetically sealed with a lid, before pasteurization - sterilization (canning), vacuum packaging and preservation.

The present invention relates, more particularly, to a method for manufacturing a closure system, of the lid type, in a multilayer material consisting of at least one EVOH (ethylene vinyl alcohol) layer sandwiched between two layers of thick polypropylene, said method also including the integration, preferably in an automated manner, of a seal at the level of the internal surface of the lid, intended to come into contact with a container to be closed.

Traditionally, in the state of the art, in order to preserve various foods, it has been known for many years to place them in containers, in particular jars, generally made of glass, before hermetically closing them using a lid and then sterilizing them at a temperature above 100°C, or pasteurizing them at a temperature below or equal to 100°C.

This step can be carried out in particular using an autoclave sterilizer, and allows a significant reduction in the load of microorganisms present in the product and/or the basic food preparation, thus avoiding any microbial development, for a more or less long-term preservation of food depending on the heat treatment applied. This step requires the container to be vacuum-packed beforehand with this closing device.

However, the closure of glass jars, with a separate lid and seal, is currently encountering a problem, in particular in the installation of the seal and in the positioning of the lid, with said seal, on the upper part, or ring, of the jar.

In fact, fitting the seal to the underside of a glass lid is a job that can only be done manually and individually for each jar to be prepared, therefore requiring a large number of personnel.

The same applies to placing the lid with the seal on the jar.

In addition, the lid, fitted with the seal, must be held, for example by means of at least two clips, or by a metal handle, on the jar, during the sterilization (canning) or pasteurization phase, the clips being able to be removed after cooling.

However, the installation of the seal on the lower face of the lid, as well as the installation of the lid and the seal on the container, are operations that are difficult to automate, which generates significant labor costs for the user, and is detrimental to the development of ranges of food products in such containers in industrial or semi-industrial environments.

As a result, the implementation of this type of glass jar is neglected by manufacturers, but also by craftsmen, the process of placing the seal on the lid, and of the assembly thus constituted on the jar, being time-consuming and complicated.

It should also be noted that the use of glass for the lid is a source of fragility during handling.

Also, the lid is, in some cases, as heavy or even heavier than the jar itself, especially when the latter consists of a small model of jar.

Another disadvantage of this type of jar once sterilized is that, after the first opening, a jar closed with a removable and separate lid, with seal, can no longer be closed semi-tight for staggered consumption, once the jar has been opened.

The present invention aims to remedy, at least in part, the drawbacks of the exclusively manual methods of fitting a seal to a lid and fitting the lid and seal assembly to the ring of the jar implemented in the prior art, by proposing a method of manufacturing a watertight, pasteurizable and sterilizable closure system for jars with a separate lid made of a multi-layer plastic material.

For this purpose, the invention relates, more particularly, to a method for manufacturing a sealed, pasteurizable and sterilizable closure system comprising a lid and a seal, intended to hermetically close a container, in particular a glass jar, said seal being positioned at the edge of an upper ring included in said container, said method being characterized in that it comprises, at least, the following steps, taken in order:

– formation, by extrusion, of a multilayer mother roll comprising at least two layers of polypropylene (PP) resistant to a temperature between 100°C and 150°C, which surround a central barrier layer of ethylene vinyl alcohol (EVOH), said multilayer mother roll being suitable for food contact;

– thermoforming and cutting, from said multi-layer mother roll, of the lid, by means of forming molds, so that said lid obtained comprises, at least, at its lower face, a circular groove constituting a housing for the seal intended to come into contact with the edge of the upper ring of the container, a central portion of said lid forming a convex dome raised outwards before vacuuming and capable of retracting to become concave during vacuuming, while a circular groove surrounding the convex dome is provided at the upper face of the lid, the latter being furthermore provided over its entire periphery with a closing rim comprising a plurality of closing notches capable of cooperating with said upper ring of said container;

– depositing said sealing gasket in the circular groove on the lower face of the cover to obtain said watertight, pasteurizable and sterilizable closing system;

– possibly, cooling of said watertight, pasteurizable and sterilizable closure system.

According to examples of implementation of the process:

- said seal is a preformed seal.

- said sealing gasket is deposited in liquid or pasty form in said circular groove, before a polymerization phase.

In an alternative embodiment of the method of the invention, in the first step thereof, there is formation, by extrusion, of a multilayer mother roll PP-EVOH-PP-flexible polymer, the layer of flexible polymer constituting the sealing gasket in the circular groove.

According to examples of implementation of the process, both when the sealing gasket is deposited in the circular groove, and when it is directly integrated into the multi-layer mother roll:

- the polypropylene layer contains color pigments.

- the EVOH barrier layer has a thickness between 10 µm and 10% of the total thickness of the multi-layer mother roll.

- said cover obtained by thermoforming also includes an opening tab.

- said cover obtained by thermoforming also includes a conical finishing edge forming a flare at the upper face of the cover.

The invention also relates to a watertight, pasteurizable and sterilizable closure system capable of being obtained using the manufacturing method according to the invention.

This comprises a lid and a seal, intended to hermetically close a container, in particular a glass jar, said seal being then positioned at the edge of an upper ring that said container comprises, said closure system being characterized in that said lid is made of multilayer plastic material suitable for food contact and comprising at least two layers of polypropylene (PP) resistant to a temperature between 100°C and 150°C and framing a barrier layer of ethylene vinyl alcohol (EVOH), said lid comprising at least, at its lower face, a circular groove constituting the housing in which the seal is placed, a central portion of said lid forming a convex dome raised towards the outside before vacuuming and capable of retracting to become concave during vacuuming, while a circular groove surrounding the convex dome is provided at the upper face of the lid, the latter being furthermore provided, over its entire periphery, with a closing rim in the form of a skirt comprising a plurality of closing notches capable of cooperating with said upper ring of said container.

Preferably, the closing system has the following additional characteristics:

– it is provided with a conical finishing rim forming at the level of the upper face of the cover, at the base of the thermoformed cover, for cooperation with the external surface of the circular groove of a second closing system when they are stacked.

- said cover has a side opening tab.

Other aims and advantages of the present invention will appear during the description which follows relating to embodiments which are given only as indicative and non-limiting examples.

Understanding of this description will be facilitated by referring to the attached drawings in which:

represents a schematic view from above (left) and along section BB (right) of an embodiment of a watertight, pasteurizable and sterilizable closure system, capable of being obtained by means of the implementation of the manufacturing method in accordance with the present invention, intended to seal a container, such as a glass jar, comprising a lid and a sealing gasket inserted in a circular groove included in the lower face of said lid, said gasket being intended to come into contact with the edge of an upper ring included in the glass jar to seal it hermetically after placing under vacuum.

represents a top photograph of a watertight, pasteurizable and sterilizable closure system capable of being obtained according to the manufacturing process of the invention, and comprising, laterally, an opening tab, and the central portion of the cover of which has the shape of a convex dome raised outwards, relative to the container, before the latter is placed under vacuum.

represents a top photograph of the watertight, pasteurizable and sterilizable closure system similar to that of the , after the container has been vacuum-packed, the central portion of the lid in the form of a convex dome raised outwards before vacuum-packing having retracted inwards to become concave during vacuum-packing.

represents a photograph of the underside of the cover, with the seal arranged in the circular groove to form the closure system of the invention.

With reference to the figures of the attached drawings, the present invention relates, more particularly, to a method of manufacturing a watertight, pasteurizable and sterilizable closure system 1.

This system 1 is intended to close the edge of a container 4, such as a jar, in particular made of glass or a plastic material, before vacuum preservation, pasteurization or sterilization of the assembly constituted by said container 4 associated with its closing system 1, said container 4 having been previously partially filled with a food product that it is desired to preserve.

Such a watertight, pasteurizable and sterilizable closure system 1 essentially comprises a cover 2, as well as a seal 3 positioned at the lower face 21 of said cover 2, in other words the face 21 intended to come into contact with the edge of the container 4.

More specifically, when positioning the closure system 1 on the container 4 to close it, said seal 3 comes into contact with the edge of an upper ring, or upper rim, not visible in the figures, to allow hermetic closure of the container 4 by placing it under vacuum before pasteurization or sterilization of the assembly.

In a first step of the manufacturing process of a closure system 1 according to the invention, a multi-layer mother roll is formed by extrusion.

This mother roll thus comprises at least two layers of polypropylene (PP) sandwiching a “barrier layer” made of ethylene vinyl alcohol (EVOH).

The PP used for the two outer layers of the multi-layer mother roll consists of a so-called “high temperature” PP, i.e. capable of withstanding temperatures of at least 125°C during heat treatment, and up to 150°C maximum in the short term, depending on technical constraints.

The EVOH barrier layer framed by said two external layers of high-temperature PP has a thickness of between 10µm and 10% of the total thickness of the PP-EVOH-PP film.

The multi-layer roll is formed by extrusion and during this process, the two materials PP and EVOH will overlap and bond together during cooling.

PP thicknesses may vary depending on the technical constraints of the container 4, in particular depending on the diameter of the latter.

It should be noted that it is essential that the multilayer material, made of PP and EVOH, be suitable for food contact, as is the material from which the sealing gasket 3 is made, the latter being able to be, in particular, silicone, rubber, or any other material suitable for this purpose.

In an advantageous embodiment of the method of the invention, the polypropylene layer extruded during the first step of the method, for the formation of the multilayer roll, may comprise color pigments.

Indeed, advantageously, by means of the method of manufacturing closure systems 1 of the invention, the latter can be personalized, the cover 2 thus being able to have different colors or logos.

Most preferably, the central EVOH barrier layer of the multilayer roll obtained following the first step of the manufacturing process of the invention has a thickness of between 10 µm and 10% of the total thickness of the film, this thickness of the EVOH barrier layer being, even more preferably, of the order of, or equal to, 80 µm.

The thickness of the EVOH barrier layer can however vary depending on the technical constraints of the container.

A second step in the manufacturing process of the invention consists of thermoforming the element and cutting it, using a forming mold, to obtain the cover 2 at the end of the process.

It should be noted that this thermoforming operation is carried out using the mold in such a way that said cover 2 finally obtained comprises, at least, at its lower face 21, a circular groove 5 constituting a housing for said sealing gasket 3 which is intended to come into contact with the edge of the upper ring of the container 4 at the time of closing of the latter by the system 1.

Furthermore, a central circular portion 23 of said cover 2 forms, after thermoforming, a convex dome 23a raised outwards, relative to the container 4 once the closure system 1 is positioned on the open part thereof, before placing under vacuum the assembly constituted by the container 4 and the closure system 1 of the latter.

Said circular central portion 23 in the form of a convex dome 23a is furthermore capable of retracting to become concave 23b when the container 4 is placed under vacuum, in particular by heat treatment of the assembly.

A circular groove 24 surrounding the convex dome 23a, at the level of the upper face 22 of the cover 2, makes it possible to limit the deformation of the latter under the action of the vacuum to only the portion of this dome 23a.

This prevents the formation of folds in the peripheral area of the cover 2, in particular in the area where said cover 2 cooperates with the seal 3.

Indeed, the presence of folds in the circular groove 5 constituting the housing of the sealing gasket 3 would have the effect of allowing air to circulate between the inside and the outside of the closed container and, consequently, a loss of vacuum.

It should also be noted that the thermoforming operation must make it possible to obtain a cover 2 whose closing edge 6, in the form of a skirt intended to cover and cooperate with the upper ring of the container 4, comprises, regularly distributed over its entire periphery, a plurality of internal closing notches 61.

In the example of realization illustrated on the In the attached non-limiting drawings, six closing notches 61 are shown.

Such internal closing notches 61 allow, once the closing system 1 has been removed from the container 4 for a first consumption of a part of the food product located inside it, to reposition said closing system 1 in a partially sealed manner.

In fact, the sealing after first opening, permitted by the presence of the notches 61 when closing the jar 4, was estimated at approximately 90%, compared to a total seal after placing under vacuum, constituting a particularly interesting seal for this type of product.

Most preferably, and as illustrated in figures 2, 3 and 4, the thermoforming step makes it possible to obtain a lateral opening tab 7 at the level of the cover 2, facilitating the first opening and the venting of the container 4 to allow the consumption of the food product contained therein.

Following the thermoforming step and obtaining the cover 2, the next step of the manufacturing process according to the invention consists of depositing the sealing gasket 3 in the circular groove 5 reserved at the level of the lower face 21 of the cover 2.

Two types of gaskets 3 can be placed in the circular groove 5.

In a first, particularly preferred example, a preformed and ready-to-use sealing gasket 3 can be deposited, either mechanically or manually, in said groove 5.

The seal 3 can be obtained here by injection of a flexible material (in particular silicone) or cut from sheets/plates of silicone or rubber (in particular natural).

In this case, the seal 3 is secured to the cover 2 by means of a plurality of micro-hooks, in the form of undercuts in the circular groove 5.

In another exemplary embodiment, it may be a sealing gasket 3 deposited in liquid or pasty form in said groove 5, which will require conformation so that the face of the gasket 5 which must cooperate with the edge of the container 4 is geometrically suitable for this cooperation, then a polymerization phase, which will depend on the polymer, the latter being able in particular to consist of silicone.

Polymerization allows the change of state of the seal 3.

Indeed, during this step, said seal 3 passes from a viscous phase to an elastic phase.

Depending on the material of the seal, such polymerization is carried out either by temperature, or by chemical reaction between two components, or even by crosslinking, in the case of rubber.

In an alternative embodiment of the manufacturing method of the invention, a flexible PP-EVOH-PP-polymer multilayer film is extruded. Thermoforming and then cutting then make it possible to obtain a part directly equipped with the sealing function, the flexible polymer layer here constituting the sealing gasket 3.

This gives said watertight, pasteurizable and sterilizable closure system 1 consisting of the cover 2 and said sealing gasket 3.

Particularly advantageously, thanks to the method of manufacturing a closure system 1 for a container 4 intended for preserving food, the step of removing the sealing gasket 3 at the lower face 21 of the cover 2 can be carried out in a fully automated manner.

This eliminates the need to use labour specifically for this step, unlike what is currently done in the state of the art, to obtain glass jars containing food ready to be preserved under vacuum or heat treated.

During the final stage of the manufacturing process of the watertight, pasteurizable and sterilizable closure system 1 of the invention, in particular following polymerization, said system 1 is cooled.

The closure systems 1 of jars 4 thus manufactured can, thus, advantageously, be stacked in a subsequent and optional step, for use with automated unstackers, to automatically close containers 4 filled with food products.

Thus, the method of the invention is particularly interesting for the development of the industrialization of food products contained in jars 4, in particular glass, sealed tightly before placing the latter under vacuum, for optimal preservation of said products under aseptic conditions.

Indeed, on the one hand, the method of the invention eliminates the currently existing step of manually fitting the seal to the lower face of the lid, as well as the fitting and removal of the clips to hold the seal and lid assembly on the jar.

The manufacture of the closing system 1 by the method of the invention allows complete automation of the closing cycle of the containers 4, by means of existing machines, which may be modified if necessary.

The closure systems 1 thus obtained can also be used with conventional chamber vacuum machines, while manual application of the lid also remains possible for vacuum packaging.

The airtight, pasteurizable and sterilizable closure systems 1 can be manufactured in such a way that they can be adapted to different types of jars 4, in particular different sizes, without modifying the latter.

The covers 2 can also be easily personalized, by adding the manufacturer's logo and/or by personalizing the color of the polypropylene mother sheath.

After a first opening, a container 4 can be resealed by the closing system 1 obtained by implementing the method of the invention, with satisfactory sealing for such a new closing operation and short-term storage.

The manufacture of such closure systems 1, based on plastic materials, which are also recyclable, allows a reduction in the weight of the jar and lid assembly, in comparison with existing assemblies made entirely of glass.

Thus, the method of the invention makes it possible to obtain closure systems 1 allowing optimal and aesthetic sealing of the edge of a container 4.

It should be noted that such systems 1 can be used both for simple vacuum packaging of jars without heat treatment, with the advantages of vacuum packaging, and for pasteurization, with medium-term preservation while respecting the cold chain, or even for sterilization of jars 4 with long-term preservation at room temperature.

The present invention then also relates to a watertight, pasteurizable and sterilizable closure system 1 capable of being obtained by implementing the manufacturing method as described above.

According to the invention, such a closing system 1 comprises, on the one hand, a cover 2 and, on the other hand, a seal 3, intended to hermetically close a container 4, such as a glass or plastic jar, said seal 3 being intimately associated with the cover 2.

According to a characteristic of the present invention, said cover 2 is made of a multilayer plastic material, suitable for food contact, and comprising at least two layers of high temperature PP framing an EVOH barrier layer of a thickness varying according to the technical constraints.

Said cover 2 has at least, at the level of its lower face 21, intended to come into contact with the edge of the container 4, a circular groove 5 constituting the housing in which the sealing gasket 3 is placed.

Essentially, a circular central portion 23 of said cover 2 forms a convex dome 23a, raised outwards, relative to the container 4, before vacuuming and capable of retracting to become concave 23b, towards the inside of said container 4, once vacuuming has been carried out.

Such a feature, namely the passage of the circular central portion 23 of the cover 2 from a convex shape to a concave shape, allows a visual control of the vacuuming of the container 4, as well as a monitoring of the maintenance of the vacuum, by analysis of the deformation.

A circular groove 24 which surrounds this circular central portion 23, capable of changing from a convex shape 23a to a concave shape 23b, is provided at the level of the upper face 22 of the cover 2.

The cover 2 of the closure system 1 is also provided, over its entire perimeter, with a closure rim 6, in the form of a skirt intended to cover the upper ring of the container, and comprising a plurality of closure notches 61 capable of cooperating with this ring for optimal sealing of the latter after the first opening.

All preferentially, and as visible in particular on the , the thermoformed cover 2 also comprises, at its external face 22, a conical finishing rim 8 at the base of the thermoformed cover 2, this conical rim 8 forming a flare, so as to allow the cooperation of a first closure system 1 with the external surface of the circular groove 5 of a second similar closure system 1, to guarantee a stable stacking of these closure systems 1, before their placement on the edge of the container 4.

By means of this feature, it is possible to work on the removal of closing systems 1 in an automated manner, in stacks, for future loaders or destackers.

It should be noted that the characteristics which have been described in the present application in connection with the method of manufacturing the closure systems 1 are applicable to the closure systems 1, capable of being obtained by means of the present method, or by another method, and vice versa.

Claims (11)

Method for manufacturing a watertight, pasteurizable and sterilizable closure system (1), comprising a lid (2) and a seal (3), intended to hermetically close a container (4), in particular a glass jar, said seal (3) being positioned at the edge of an upper ring included in said container (4), said method being characterized in that it comprises, at least, the following steps, taken in order:
- formation, by extrusion, of a multilayer mother roll comprising at least two layers of polypropylene (PP) resistant to a temperature between 100°C and 150°C, which surround a central barrier layer of ethylene vinyl alcohol (EVOH), said multilayer mother roll being suitable for food contact;
- thermoforming and cutting, from said multilayer mother roll, the cover (2), by means of forming molds, so that said cover (2) obtained comprises, at least, at its lower face (21), a circular groove (5) constituting a housing for the seal (3) intended to come into contact with the edge of the upper ring of the container (4), a central portion (23) of said cover (2) forming a convex dome (23a) raised outwards before vacuuming and capable of retracting to become concave (23b) during vacuuming, while a circular groove (24) surrounding the convex dome (23a) is formed at the upper face (22) of the cover (2), the latter being moreover provided over its entire periphery with a closing rim (6) comprising a plurality of closing notches (61) capable of cooperating with said upper ring of said container (4);
- depositing said sealing gasket (3) in the circular groove (5) of the lower face of the cover to obtain said watertight, pasteurizable and sterilizable closing system (1);
- possibly, cooling of said watertight, pasteurizable and sterilizable closure system (1). Method of manufacturing a watertight, pasteurizable and sterilizable closure system (1) according to claim 1 characterized in that said sealing gasket (3) is a preformed gasket. Method for manufacturing a watertight, pasteurizable and sterilizable closure system (1) according to claim 1, characterized in that said sealing gasket (3) is deposited in liquid or pasty form in said circular groove (5), before a polymerization phase. Method for manufacturing a watertight, pasteurizable and sterilizable closure system (1), comprising a lid (2) and a seal (3), intended to hermetically close a container (4), in particular a glass jar, said seal (3) being positioned at the edge of an upper ring included in said container (4), said method being characterized in that it comprises, at least, the following steps, taken in order:
- formation, by extrusion, of a multilayer mother roll comprising at least two layers of polypropylene (PP) resistant to a temperature between 100°C and 150°C, which frame a central barrier layer of ethylene vinyl alcohol (EVOH), and a layer of flexible polymer constituting said seal, said multilayer mother roll being suitable for food contact;
- thermoforming and cutting, from said multilayer mother roll, the cover (2), by means of forming molds, so that said cover (2) obtained comprises, at least, at its lower face (21), a circular groove (5) constituting a housing for the seal (3) constituted by the flexible polymer layer of the multilayer roll, said seal (3) being intended to come into contact with the edge of the upper ring of the container (4), a central portion (23) of said cover (2) forming a convex dome (23a) raised outwards before vacuuming and capable of retracting to become concave (23b) during vacuuming, while a circular groove (24) surrounding the convex dome (23a) is formed at the upper face (22) of the cover (2), the latter being moreover provided over its entire periphery with a closing rim (6) comprising a plurality of closing notches (61) able to cooperate with said upper ring of said container (4);
- possibly, cooling of said watertight, pasteurizable and sterilizable closure system (1). Method of manufacturing a watertight, pasteurizable and sterilizable closure system (1) according to any one of the preceding claims, characterized in that the polypropylene layer is customizable and includes color pigments. Method of manufacturing a sealed, pasteurizable and sterilizable closure system (1) according to any one of the preceding claims, characterized in that the EVOH barrier layer has a thickness of between 10 µm and 10% of the total thickness of the multi-layer mother roll. Method of manufacturing a watertight, pasteurizable and sterilizable closure system (1) according to any one of the preceding claims, characterized in that said cover (2) obtained by thermoforming also comprises an opening tab (7). Method of manufacturing a watertight, pasteurizable and sterilizable closure system (1) according to any one of the preceding claims, characterized in that said cover (2) obtained by thermoforming also comprises a conical finishing rim (8) forming a flare at the upper face (22) of the cover (2). A sealed, pasteurizable and sterilizable closure system (1) obtainable by implementing the manufacturing method according to any one of the preceding claims, comprising a lid (2) and a seal (3), intended to hermetically close a container (4), in particular a glass jar, said seal (3) then being positioned at the edge of an upper ring that said container (4) comprises, said closure system (1) being characterized in that said lid (2) is made of a multilayer plastic material suitable for food contact and comprising at least two layers of polypropylene (PP) resistant to a temperature between 100°C and 150°C and framing a barrier layer of ethylene vinyl alcohol (EVOH), said lid (2) comprising at least, at its lower face (21), a circular groove (5) constituting the housing in which the seal (3) is placed, a central portion (23) of said lid (2) forming a convex dome (23a) raised towards the exterior before vacuuming and capable of retracting to become concave (23b) during vacuuming, while a circular groove (24) surrounding the convex dome (23a) is provided at the level of the upper face (22) of the cover (2), the latter being furthermore provided, over its entire periphery, with a closing rim (6) in the form of a skirt comprising a plurality of closing notches (61) capable of cooperating with said upper ring of said container (4). Watertight, pasteurizable and sterilizable closure system (1) according to the preceding claim, characterized in that it is provided with a conical finishing rim (8) forming at the level of the upper face (22) of the cover (2), at the base of the thermoformed cover (2), for cooperation with the external surface of the circular groove (5) of a second closure system (1) when they are stacked. Watertight, pasteurizable and sterilizable closure system (1) according to claim 9 or claim 10, characterized in that said cover (2) has a lateral opening tab (7).